The present invention relates to the field of obstetrics and particularly to methods and devices useful in prenatal identification of meconium in amniotic fluid.
Amniotic fluid is a liquid that surrounds and protects the fetus inside the amniotic sac within the uterus.
During gestation, the colon of a fetus fills with meconium, fetal feces comprising bile and its metabolites, gastrointestinal and pancreatic secretions, mucus, cellular debris, swallowed vernix caseosa, lanuge, and blood. Usually, the fetus is continent until birth, but in a significant minority of births (7-22%) it is observed that the fetus has excreted a significant amount of meconium into the amniotic fluid leading to meconium-stained amniotic fluid (MSAF).
The pathophysiology of meconium excretion into the amniotic fluid is not entirely understood but it has been suggested that in some cases, the meconium excretion is caused by fetal distress due to, for example, acute or chronic fetal hypoxia.
Meconium present in the amniotic fluid apparently has a detrimental effect on the fetus, for example causing umbilical vessel constriction, vessel necrosis, and production of thrombi, potentially associated with ischemic cerebral palsy. Meconium alters the level of zinc in amniotic fluid, which may reduce the antibacterial properties of amniotic fluid, potentially facilitating intra-amniotic infection. Meconium has also been implicated as leading to other adverse effects, for example, increased preterm labor, altered coagulation profile in the fetus and neonatal seizures. Although the direct and indirect effects remain uncertain, MSAF is consistently identified as a predictor of maternal and perinatal complications with increased fetal risk, especially when fetal exposure time has been extended and the fluid is concentrated. It has been demonstrated that infants born in the presence of MSAF have lower overall infant assessment scores in comparison to newborns without meconium staining.
5-20% of infants born with meconium-stained amniotic fluid have meconium aspiration syndrome where meconeal particles enter the fetal lungs, leading to severe respiratory disorders. Infants with severe meconium aspiration syndrome develop pulmonary hypertension, progressive respiratory distress, hypoxia, hypercapnia, and acidosis. Infant mortality from meconium aspiration syndromes accounts for 2% of all perinatal deaths in developed countries.
A number of methods and devices are known for identifying the presence of meconium in amniotic fluid.
Amniocentesis is an invasive sampling technique which has become established in obstetric care for prenatal genetic testing (karyotyping).
In U.S. Pat. No. 5,361,759 is taught an invasive method for detection of meconium, blood or vernix in amniotic fluid by absorbance spectroscopy of a sample of amniotic fluid acquired by penetrating an amniotic sac.
In U.S. Pat. No. 5,713,351 is taught an invasive method for the detection of meconium or blood in amniotic fluid by penetrating an amniotic sac with a probe and withdrawing amniotic fluid through the lumen of the probe into an observation chamber.
In amnioscopy, a health-care professional directly observes the forebag of an amniotic sac through a dilated cervix to look for meconium staining. Although useful in identifying heavy staining, amnioscopy has not proven effective in identifying milder cases of staining. Amnioscopy requires an undesirable degree of cervical dilation.
In U.S. Pat. No. 5,172,693 is taught non-invasive detection of meconium in amniotic fluid held in an amniotic sac based on detecting fluorescence of the bilirubin component of meconium in meconium-stained amniotic fluid. A probe is placed against the body (preferably the uterine wall) and monochromatic excitation light at a wavelength of 488 nm or 514 nm (produced by an argon laser) is projected from the probe through the body tissue into the amniotic sac. If present in the amniotic fluid, bilirubin absorbs the excitation light and emits characteristic fluorescence.
It would be highly advantageous to have a method for detecting the presence of meconium in amniotic fluid having advantages over the methods known in the art.